Apparatus for sensing position and/or torque

ABSTRACT

An apparatus for measuring relative displacement between a first shaft and a second shaft includes first and second rotor assemblies. The first rotor assembly is coupled to the first shaft and is centered on an axis. The second rotor assembly is coupled to the second shaft. The second rotor assembly has first and second stator plates. Each of the first and second stator plates includes an upper surface and a lower surface. The upper and lower surfaces are parallel. The first and second stator plates include a plurality of teeth extending in a direction radial of the axis. The first and second stator plates form a gap between the lower surface of the first stator plate and the upper surface of the second stator plate. The apparatus further includes at least one magnet having a magnetic field and disposed on the first rotor assembly and a sensing device disposed within the gap for sensing a magnetic flux of the magnetic field.

[0001] This application claims priority to U.S. Provisional PatentApplication Ser. No. 60/477,482 filed Jun. 10, 2003, and U.S.Provisional Patent Application Ser. No. 60/542,511 filed Feb. 6, 2004.

FIELD OF THE INVENTION

[0002] The present invention relates generally to apparatus for sensingposition and/or torque and more particularly to an apparatus for sensingangular displacement between first and second rotating shafts.

BACKGROUND OF THE INVENTION

[0003] It is frequently important to measure or sense an angulardisplacement and/or relative torque between first and second shafts. Therelative displacement may be measured by a small angle displacementsensor. The relative position may then be used to derive the torqueapplied between the two shafts.

[0004] For example, power steering systems in motor vehicles and thelike are designed to provide appropriate hydraulic or electrical assistto allow a driver to complete a turn of the motor vehicle. The drivertypically turns a steering wheel which is connected to a first shaft.The first shaft is coupled to a second shaft which is connected to asteering mechanism. The first and second shafts may be coupled by acompliant member, such as a torsion bar. Typically, the first shaft mayrotate with respect to the second shaft by a predetermined number ofdegrees, e.g., +/−12 degrees. Mechanical stops may prevent furthermovement. The amount of assist is determined as a function of the amountof torque being applied to the first shaft.

[0005] Many types of position sensors utilize one or more magnets forgenerating a magnetic field. The magnetic circuit typically includes asecond magnetic structure which forms a gap. A sensing device, disposedwithin the gap, detects changes in the magnetic flux which is used as anindication of the relative displacement between the first and secondshafts.

[0006] One such system is disclosed in US Patent Application20040011138, published Jan. 22, 2004 (hereafter “Gandel”). The secondmagnetic structure in Gandel is made up of two ferromagnetic rings, eachhaving a plurality of axially oriented teeth. Each rings includes acircular flux-closing zone, which is parallel to the flux-closing zoneof the other ring. The teeth of the rings are generally perpendicular tothe flux-closing zones and are interleaved.

[0007] One inherent problem with the Gandel device is that it issensitive to mechanical misalignment during assembly. Specifically, theaxial teeth of the rings require very accurate placement with respect toeach other. A deviation in the relative position of the rings and teethwith respect to each other will cause reduced performance of the device.It is difficult to accurately align the teeth of the rings and tomaintain their relative position to maintain the correct distance fromtooth to tooth.

[0008] Another disadvantage of the Gandel device is that it is sensitiveto mechanical variation during operation. The device is sensitive toangular and parallel changes in the relationship of the two rotors toone another. Mechanical variation in these two directions will causevariation in the output.

[0009] Another disadvantage of the Gandel device is an output variationover 360°. This variation is caused by the magnetic structure of thedevice and the measurement location of the magnetosensitive elements.

[0010] Another inherent problem with the rings of the Gandel device isthat they are complex and difficult and costly to manufacture.

[0011] The present invention is aimed at one or more of the problemsidentified above.

SUMMARY OF THE INVENTION

[0012] In a first aspect of the present invention, a rotor assembly foruse in a sensor for measuring relative position between first and secondshaft is provided. The rotor assembly includes first and second statorplates. The first stator plate has an upper surface and a lower surface.The second stator plate has an upper surface and a lower surface. Thefirst and second stator plates include a plurality of teeth extending ina direction radial of an axis. The first and second stator plates form agap between the lower surface of the first stator plate and the uppersurface of the second stator plate. The gap has a uniform thickness. Therotor assembly further includes a retaining member to hold theorientation and spacing of the first and second stator plates relativeto each other.

[0013] In a second aspect of the present invention, a rotor assembly foruse in a sensor for measuring the relative position between first andsecond shafts is provided. The rotor assembly includes a rotor centeredon an axis. The rotor has an inner surface and an outer surface. Theouter surface forms at least one slot associated with an outer radius.The inner surface forms at least one support structure associated withan inner radius.

[0014] In a third aspect of the present invention, an apparatus formeasuring relative position between a first shaft and a second shafts isprovided. The apparatus includes first and second rotor assemblies. Thefirst rotor assembly is coupled to the first shaft and is centered on anaxis. The second rotor assembly is coupled to the second shaft. Thesecond rotor assembly has first and second stator plates. Each of thefirst and second stator plates includes an upper surface and a lowersurface. The upper and lower surfaces are parallel. The first and secondstator plates include a plurality of teeth extending in a directionradial of the axis. The first and second stator plates form a gapbetween the lower surface of the first stator plate and the uppersurface of the second stator plate. The apparatus further includes atleast one magnet having a magnetic field and disposed on the first rotorassembly and at least one sensing device disposed within the gap forsensing a change in the magnetic field.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Other advantages of the present invention will be readilyappreciated as the same becomes better understood by reference to thefollowing detailed description when considered in connection with theaccompanying drawings wherein:

[0016]FIG. 1A is an illustration of an apparatus for sensing a relativeposition between a first shaft and a second shaft, according to anembodiment of the present invention;

[0017]FIG. 1B is an enlarged illustration of the position sensingapparatus of FIG. 1A;

[0018]FIG. 1C is a three-dimensional illustration of the positionsensing apparatus of FIG. 1A in a housing;

[0019]FIG. 1D is a top view of the apparatus and housing of FIG. 1C;

[0020]FIG. 2A is a first cut away view of the apparatus of FIG. 1A;

[0021]FIG. 2B is a second cut away view of the apparatus of FIG. 1A;

[0022]FIG. 2C is a cut away view of a portion of a rotor assembly of theapparatus of FIG. 1A;

[0023]FIG. 2D is a second cut away view of a portion of a rotor assemblyof the apparatus of FIG. 1A;

[0024]FIG. 3A is a three-dimensional view of a portion of a first andsecond rotor assembly of the apparatus of FIG. 1A;

[0025]FIG. 3B is a diagrammatic illustration of a position sensor andthe apparatus of FIG. 1A;

[0026]FIG. 3C is a diagrammatic illustration of a position sensor withtwo sensing devices, according to an embodiment of the presentinvention;

[0027]FIG. 3D is a diagrammatic illustration of a position sensor withtwo sensing devices, according to an embodiment of the presentinvention;

[0028]FIG. 3E is an exemplary graph illustrating operation of theposition sensor of FIG. 3C;

[0029]FIG. 3F is an exemplary graph illustrating operation of theposition sensor of FIG. 3D;

[0030]FIG. 4 is a top view of the first and second rotor assemblies ofFIG. 3A;

[0031]FIG. 5 is a side view of the first and second rotor assemblies ofFIG. 3A;

[0032]FIG. 6 is an exemplary graph illustrating angle versus fluxdensity of the apparatus of FIG. 1A;

[0033]FIG. 7A is a three-dimensional illustration of a first rotorassembly of the apparatus of FIG. 1A, according to an embodiment of thepresent invention;

[0034]FIG. 7B is a cut away view of the first rotor assembly FIG. 7A;

[0035]FIG. 7C is a side view of the first rotor assembly of FIG. 7A;

[0036]FIG. 7D is a diagrammatic illustration of a portion of a rotor ofthe first rotor assembly of FIG. 7A;

[0037]FIG. 8A is an illustration of a tooth of the second rotor assemblyaccording to an embodiment of the present invention;

[0038]FIG. 8B is an illustration of a tooth of the second rotor assemblyaccording to another embodiment of the present invention;

[0039]FIG. 8C is an illustration of a tooth of the second rotor assemblyaccording to a further embodiment of the present invention;

[0040]FIG. 8D is an illustration of a tooth of the second rotor assemblyaccording to still another embodiment of the present invention;

[0041]FIG. 9A is a diagrammatic illustration of a cut away view of asecond rotor assembly of the apparatus of FIG. 1A, according to a firstembodiment of the present invention;

[0042]FIG. 9B is a top view of a portion of the second rotor assembly ofFIG. 9A;

[0043]FIG. 9C is a front view of the second rotor assembly of FIG. 9A;

[0044]FIG. 10A is a diagrammatic illustration of a cut away view of asecond rotor assembly of the apparatus of FIG. 1A, according to a secondembodiment of the present invention;

[0045]FIG. 10B is a top view of a portion of the second rotor assemblyof FIG. 10A;

[0046]FIG. 10C is a front view of the second rotor assembly of FIG. 10A;

[0047]FIG. 11A is a diagrammatic illustration of a second rotor assemblyof the apparatus of FIG. 1A, according to a third embodiment of thepresent invention;

[0048]FIG. 11B is a partial top view of the second rotor assembly ofFIG. 11A;

[0049]FIG. 11C is a front view of the second rotor assembly of FIG. 11A;

[0050]FIG. 11D is a top view of the second rotor assembly of FIG. 11A;

[0051]FIG. 11E is a three dimensional view of the second rotor assemblyof FIG. 11A;

[0052]FIG. 12A is a top view of a square magnet;

[0053]FIG. 12B is a side view of the magnet of FIG. 12A;

[0054]FIG. 12C is a top view of a plurality of magnets arranged inparallel rows;

[0055]FIG. 12D is a side view of the magnet of FIG. 12C;

[0056]FIG. 12E is a three-dimensional view of a ring magnet with aplurality of north-south pole pairs;

[0057]FIG. 13 is a diagrammatic illustration of a cross-sectional viewof the apparatus of FIG. 1A, according to a first embodiment of thepresent invention;

[0058]FIG. 14 is a diagrammatic illustration of a cross-sectional viewof the apparatus of FIG. 1A, according to a second embodiment of thepresent invention;

[0059]FIG. 15 is a diagrammatic illustration of a cross-sectional viewof the apparatus of FIG. 1A, according to a third embodiment of thepresent invention;

[0060]FIG. 16 is a diagrammatic illustration of a cross-sectional viewof the apparatus of FIG. 1A, according to a fourth embodiment of thepresent invention;

[0061]FIG. 17 is a diagrammatic illustration of a cross-sectional viewof the apparatus of FIG. 1A, according to a fifth embodiment of thepresent invention;

[0062]FIG. 18 is a diagrammatic illustration of a cross-sectional viewof the apparatus of FIG. 1A, according to a sixth embodiment of thepresent invention;

[0063]FIG. 19 is a diagrammatic illustration of a cross-sectional viewof the apparatus of FIG. 1A, according to a seventh embodiment of thepresent invention;

[0064]FIG. 20 is a diagrammatic illustration of a cross-sectional viewof the apparatus of FIG. 1A, according to an eighth embodiment of thepresent invention;

[0065]FIG. 21 is a diagrammatic illustration of a cross-sectional viewof the apparatus of FIG. 1A, according to a ninth embodiment of thepresent invention;

[0066]FIG. 22 is a diagrammatic illustration of a cross-sectional viewof the apparatus of FIG. 1A, according to a tenth embodiment of thepresent invention;

[0067]FIG. 23 is a diagrammatic illustration of a cross-sectional viewof the apparatus of FIG. 1A, according to an eleventh embodiment of thepresent invention;

[0068]FIG. 24 is a diagrammatic illustration of a cross-sectional viewof the apparatus of FIG. 1A, according to a twelfth embodiment of thepresent invention;

[0069]FIG. 25 is a diagrammatic illustration of a cross-sectional viewof the apparatus of FIG. 1A, according to a thirteenth embodiment of thepresent invention;

[0070]FIG. 26 is a diagrammatic illustration of a cross-sectional viewof the apparatus of FIG. 1A, according to a fourteenth embodiment of thepresent invention;

[0071]FIG. 27 is a diagrammatic illustration of a cross-sectional viewof the apparatus of FIG. 1A, according to a fifteenth embodiment of thepresent invention;

[0072]FIG. 28 is a diagrammatic illustration of a cross-sectional viewof the apparatus of FIG. 1A, according to a sixteenth embodiment of thepresent invention;

[0073]FIG. 29 is a diagrammatic illustration of a cross-sectional viewof the apparatus of FIG. 1A, according to a seventeenth embodiment ofthe present invention;

[0074]FIG. 30 is a diagrammatic illustration of a cross-sectional viewof the apparatus of FIG. 1A, according to an eighteenth embodiment ofthe present invention;

[0075]FIG. 31 is a diagrammatic illustration of a cross-sectional viewof the apparatus of FIG. 1A, according to a nineteenth embodiment of thepresent invention;

[0076]FIG. 32 is a diagrammatic illustration of a cross-sectional viewof the apparatus of FIG. 1A, according to a twentieth embodiment of thepresent invention;

[0077]FIG. 33 is a diagrammatic illustration of a cross-sectional viewof the apparatus of FIG. 1A, according to a twenty-first embodiment ofthe present invention;

[0078]FIG. 34 is a diagrammatic illustration of a cross-sectional viewof the apparatus of FIG. 1A, according to a twenty-second embodiment ofthe present invention;

[0079]FIG. 35 is a diagrammatic illustration of a cross-sectional viewof the apparatus of FIG. 1A, according to a twenty-third embodiment ofthe present invention;

[0080]FIG. 36 is a diagrammatic illustration of a cross-sectional viewof the apparatus of FIG. 1A, according to a twenty-fourth embodiment ofthe present invention;

[0081]FIG. 37 is a diagrammatic illustration of a cross-sectional viewof the apparatus of FIG. 1A, according to a twenty-fifth embodiment ofthe present invention;

[0082]FIG. 38 is a diagrammatic illustration of a cross-sectional viewof the apparatus of FIG. 1A, according to a twenty-sixth embodiment ofthe present invention;

[0083]FIG. 39 is a diagrammatic illustration of a cross-sectional viewof the apparatus of FIG. 1A, according to a twenty-seventh embodiment ofthe present invention;

[0084]FIG. 40 is a diagrammatic illustration of a cross-sectional viewof the apparatus of FIG. 1A, according to a twenty-eighth embodiment ofthe present invention;

[0085]FIG. 41 is a diagrammatic illustration of a cross-sectional viewof the apparatus of FIG. 1A, according to a twenty-ninth embodiment ofthe present invention;

[0086]FIG. 42 is a diagrammatic illustration of a cross-sectional viewof the apparatus of FIG. 1A, according to a thirtieth embodiment of thepresent invention;

[0087]FIG. 43 is a diagrammatic illustration of a cross-sectional viewof the apparatus of FIG. 1A, according to a thirty-first embodiment ofthe present invention;

[0088]FIG. 44 is a diagrammatic illustration of a cross-sectional viewof the apparatus of FIG. 1A, according to a thirty-second embodiment ofthe present invention;

[0089]FIG. 45 is a diagrammatic illustration of a cross-sectional viewof the apparatus of FIG. 1A, according to a thirty-third embodiment ofthe present invention;

[0090]FIG. 46 is a diagrammatic illustration of a cross-sectional viewof the apparatus of FIG. 1A, according to a thirty-fourth embodiment ofthe present invention;

[0091]FIG. 47 is a diagrammatic illustration of a cross-sectional viewof the apparatus of FIG. 1A, according to a thirty-fifth embodiment ofthe present invention;

[0092]FIG. 48 is a diagrammatic illustration of a cross-sectional viewof the apparatus of FIG. 1A, according to a thirty-sixth embodiment ofthe present invention;

[0093]FIG. 49 is a diagrammatic illustration of a cross-sectional viewof the apparatus of FIG. 1A, according to a thirty-seventh embodiment ofthe present invention; and

[0094]FIG. 50 is a diagrammatic illustration of a cross-sectional viewof the apparatus of FIG. 1A, according to a thirty-eighth embodiment ofthe present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0095] With reference to the Figures and in operation, an apparatus 10senses the relative position between a first shaft 12 and a second shaft14. The relative position may then be used to derive the torque appliedbetween the first and second shafts 12, 14.

[0096] In the illustrated embodiment, the apparatus 10 may be used in anpower steering system 16 to provide a measurement of input torquegenerated by a driver turning a steering wheel (not shown). The inputtorque is used to provide appropriate hydraulic or electrical assist toallow the driver to complete a turn with minimal effort, but increasedstability. The first shaft 12 is connected to the steering wheel. Thesecond shaft 14 is coupled to a steering system (not shown), forexample, as a rack and pinion gear mechanism. As is known in the art, acompliant member such as a torsion bar 18 couples the first and secondshafts 12, 14. The first and second shafts 12, 14 are moveable relativeto each other through a predetermined range, e.g., ±8 or ±12 degrees. Itshould be noted that the range of relative movement will be dependentupon application. The present invention is not limited to any givenrange of relative movement.

[0097] Mechanical stops 20 restrict further relative movement betweenthe first and second shafts 12, 14. A position sensor may be used tomeasure rotation of the first or second shafts 12, 14. The positionsensor may be a contact or non-contact sensor. The apparatus 10 maycontained within a housing 22, which may also contain portions of thefirst and second shafts 12, 14 and components of the power steeringsystem. Such steering systems 16 are well known in the art and are,therefore, not further discussed.

[0098] In one aspect of the present invention, the apparatus 10 includesa first rotor assembly 24 and a second rotor assembly 26. The firstrotor assembly 24 is coupled to the first shaft 12 and is centered on anaxis 28. The second rotor assembly 26 is coupled to the second shaft 14.The first and second rotor assemblies 24, 26 are coaxial.

[0099] With specific reference to FIGS. 2A, 2B, 7A, 7B, 7C, the firstrotor assembly 24 includes a rotor 30 centered on the axis 28. In oneembodiment, the rotor 30 includes a plurality of slots 32. The firstrotor assembly 24 includes a plurality of magnets 34 located in eachslot 32.

[0100] The magnets 34 may be affixed or held in place in any appropriatemanner such as by an adhesive or crimping. In one aspect of the presentinvention, a retaining member 36 may be used along with, or in place of,the adhesive. The retaining member 36 is made from a non-magneticmaterial, such as plastic. In one embodiment, the retaining member 36 isovermolded the combined rotor 30 and magnets 34, once the magnets 34 areinserted into the slots 32.

[0101] With specific reference to FIGS. 2A and 2B, the first rotorassembly 24 is pressed onto the first shaft 12. As shown, the firstshaft 12 may have an enlarged portion 38 which forms a press-fit withthe first rotor assembly 24.

[0102] The first rotor 30 is composed of a soft magnetic material, suchas a nickel iron alloy. The first rotor 30 may be made using a stampingprocess or may be made from a powdered metal using a sintering processor through a machining process.

[0103] The rotor 30 includes an inner surface 40 and an outer surface42. The slots 32 are formed in the outer surface 42. The inner surface40 has an associated inner radius 44 and the outer surface 42 has anassociated outer radius 46. In between the slots 32, the rotor 30 formssupport structures 48. The inner radius 44 is defined by the innersurface 40 at the center of a support structure 48. In one aspect of thepresent invention, the inner radius 44 is greater than outer radius 46.

[0104] In the illustrated embodiment, the magnets 34 are disposed evenlyaround the circumference of the rotor 30. The spacing between, i.e., thewidth of the support structures 48, the magnets 34 are approximately thewidth of the magnets 34 or slots 32. The support structures 48 serves asthe path the magnetic flux flows through to complete the magneticcircuit on its path through the magnets 34.

[0105] As shown, in the illustrated embodiment, top surface of themagnets 34 does not protrude beyond the support structures 48 in theaxial direction.

[0106] In one embodiment, the rotor assembly 24 includes six squaremagnets 34, such as shown in FIG. 12A. The front surface of the magnet34 in FIG. 12A is square. In an alternative embodiment, the frontsurface of the magnet 34 is rectangular.

[0107] The front surface of the magnet 34 in FIG. 12A is the North poleof the magnet 34. The back surface of the magnet 34 is the South pole.In the illustrated embodiment i.e., one of the front or back surface ofthe magnet 34 is adjacent the rotor 30. Four side surfaces adjoin thefront and back surfaces of the magnets 34. At least one pair of edgesformed by one of the front and back surfaces and the four side surfacesof the magnets 34 are rounded.

[0108] In one embodiment, all of the magnets 34 on the rotor areorientated in a similar manner, i.e., one of the North pole or the Southpole is “down”, i.e., adjacent the rotor 30, and the other pole, is“up”. In another embodiment, the orientations of the magnets 34 arealternated, one magnet 34 is orientated “up” and the adjacent magnets 34are orientated “down”.

[0109] The first rotor assembly 24 may also include other magnetarrangements. For example, with reference to FIG. 12B, the rotorassembly 24 may include two adjacent rows 50, 52 of magnets 34. Each row50, 52 may include a plurality of magnets 34 spaced equidistantly aroundthe circumference of the rotor 30. Each magnet 34 in one of the rows 50,52 may be orientated in the same direction or orientated in the oppositedirection from the adjacent magnets. Alternatively, the rotor assembly24 may include one or more ring magnets 54, as shown in FIG. 12C. Thering magnet 54 has one or more pairs of adjacent poles 56, i.e., eachpair having a North pole and a South pole. The North pole of one pairbeing adjacent the South pole of the next pair. For example, the ringmagnet 54 may have six pairs of North and South poles. The ring magnet54 has an interior bore 58 which may surround the rotor 34. The ringmagnet 54 may be affixed to the rotor 34 by an adhesive and/or theretaining member 36 and/or any suitable means. If more than one ringmagnet 54 is provided, the ring magnets 54 are parallel.

[0110] The rotor 34 is designed to eliminate hoop stress. Hoop stress iseliminated by the relationship between the inner radius 44 and the outerradius 46. As shown, the rotor 34 has no sharp corners which will reducewear on any manufacturing tools. In the illustrated embodiment, eachmagnet slot 32 is defined by a plane 60. A centerpoint 62 of the plane60 is tangent to the outer radius 46. Associated with each slot 32 mayalso include stress relief slots 64. Additionally, a non-continuousinner diameter 47 may also eliminate hoop stress.

[0111] Returning to FIGS. 2A, 2B, 3A, 4 and 5, the second rotor assembly26 includes a first stator plate 66 and a second stator plate 68. Thefirst and second stator plates 66, 68 are parallel to each other. Asbest shown in FIG. 5, the first stator plate 66 includes an uppersurface 66A and a lower surface 66B. The second stator plate 68 alsoincludes an upper surface 68A and a lower surface 68B. The upper andlower surfaces 66A, 66B, 68A, 68B are parallel. The lower surface 66B ofthe first stator plate 66 faces the upper surface 68A of the secondstator plate 68, as shown. The first and second stator plates 66, 68 maybe manufactured using a stamping process may be made from a powderedmetal using a sintering process, or may be made using a machiningprocess.

[0112] As best shown in FIGS. 3A and 5, in the illustrated embodimentthe first stator plate 66 includes a circular base 66C and a pluralityof teeth 66D extending from the circular base 66C in a radial direction.Likewise, the second stator plate 68 includes a circular base 68C and aplurality of teeth 68D extending from the circular base 68C in a radialdirection.

[0113] As discussed below, the teeth 66D, 68D of the first and secondstator plates 66, 68 may be in-phase or offset from each other.

[0114] In the illustrated embodiment, the first and second plates 66, 68are planar. As shown in FIGS. 3A and 5 the upper surface of the teeth66D, 68D is co-planar with the upper surface 66A, 68A of the respectivestator plate 66, 68 and the lower surface of the teeth 66D, 68D isco-planar with the lower surface 66B, 68B of the respective stator plate66, 68. In other words, the teeth 66D on the first stator plate 66 donot axially intersect with the teeth 68D on the second stator plate 68,i.e., do not intersect with a common plane perpendicular to the axis 28.

[0115] As shown in FIG. 5, the first and second stator plates 66, 68form a gap 70 between the lower surface 66B of the first stator plate 66and the upper surface 68A of the second stator plate 68. As shown, thegap 70 has a uniform thickness.

[0116] With specific reference to FIGS. 2A, 2B, 2C, 2D, in one aspect ofthe present invention, the second rotor assembly 26 includes a retainingmember 72. The retaining member 72 is made form a non-magnetic material,such as plastic. In one embodiment, the retaining member 72 isovermolded the first and second stator plates 66, 68. The first statorplate 66 and the second stator plate 68 are retained by the retainingmember 72 which fixes the relative position thereof. The retainingmember 72 retains the first and second stator plates 66, 68 in apredetermined relationship, i.e., to maintain the size of the desiredgap 70 and the angular relationship between the first and second statorplates 66, 68.

[0117] The retaining member 72 also includes an inner bore 78. Theretaining member 72 is slipped over the second shaft 14, the inner bore78 forming a friction fit with the second shaft 14. The second shaft 14may also include a number of splines (not shown) which form a splineinterface with the retaining member 72. A retaining ring 80 fitted overan outer surface 82 of the retaining member 74 opposite the inner bore78 may be used also as a redundant feature to retain the retainingmember 72 on the second shaft 14.

[0118] With particular reference to FIGS. 1C, 1D, and 2B, the apparatus10 includes at least one sensing device 84 disposed within the gap 70for sensing a change in magnetic flux. In the illustrated embodiment,the sensing device 84, e.g., a hall effect sensor, is mounted to acircuit board 86. The sensing device 84 and the circuit board 86 arecontained with a probe housing 88. The probe housing 88 is eithermounted to a stationery member (not shown) or rotationally mounted to abearing surface (not shown) and serves to accurately position thesensing device 84 within the gap 70. A wire harness 90 provides powerand delivers signals from the sensing device 84. Alternately oradditionally, a wedge gage plate, or screws may be used to assist inaccurately positioning the sensing device 84 in the gap 70.

[0119] As discussed above, in the illustrated embodiment, the teeth 66D,68D of the first and second stator plates 66, 68 are offset orout-phase. The magnetic field measured by the sensing device 84 variesdepending on the alignment of the magnets in the first rotor assembly 24and the teeth 68D, 68D. As shown in FIG. 4, the radial gap between theteeth 66D, 68D and the top of the magnets 34 is greater than the gapbetween the teeth 66D, 68D and the top of the supporting structures 48.

[0120] The magnetic circuit formed by the magnets has mainly two regionscalled upper magnetic zone formed between upper stator and the magnetsand lower magnetic zone formed between lower stator and the magnets. Thedifferential flux between these two zones flows through the measurementslot where magnetosensitive elements sense the field. Hence at no loadtorque condition, both of the zones produce the same amount of flux,hence the differential flux crossing through the gap 70 is zero.Depending on the relative displacement (+/−8 degrees) the differentialflux either flows up or down in the measurement slot. With reference toFIG. 6, an exemplary graph of flux density measured by the sensingdevice 84 as a function of angular displacement between the first andsecond shafts 12, 14 is shown. At zero degrees, no torque is being onthe first shaft 12 and no flux is measured. As torque is applied to thefirst shaft 12, the flux density measured by the sensing device 84increases or decreases depending on the direction of travel of the firstshaft 12. As shown in the example of FIG. 6, the maximum relativedisplacement between the first and second shafts 12, 14 is +/−θ degreeswith an associated −/−G Gauss of flux density variation. It should benoted that the graph of FIG. 6 is exemplary and for illustrativepurposes only.

[0121] With particular reference to FIGS. 3C, 3D, 3E, and 3F, twosensing devices 84 may be used. Any changes in magnetic flux at constantdisplacement between the first and second rotor assemblies 24, 26 over360 degrees will have the same effect on each device 84. The spacing ofthe sensing devices 84 is dependent upon the number of magnetic polesand teeth of the first and second rotor assemblies 84, respectively. Inthe illustrated embodiment, there are six magnets associated with thefirst rotor assembly 24 and six radial teeth in each stator in thesecond rotor assembly 26. Due to this particular magnetic structure, atconstant torque conditions, the differential flux in the measurementzone will vary over 360 degrees. This variation will cause anoscillation of the output over 360 degrees which will appear with afrequency equal to the number of magnetic poles and stator teeth locatedon the first and second rotor assemblies. As shown in FIG. 3C, twosensing devices 84 may be used. In the present embodiment, thisoscillation will have a 6th order ripple and will be referred to as a “6per rev”. This six per rev will appear in the signal from both sensingdevices 84 (T1 and T2). In this case, the T1 and T2 signals haveopposite polarities. The black rectangle inside the Hall sensors 84represents the sensitive area of the device. The output signals areproportional to the normal component of the flux passing through thesensitive area. It is desirable that the oscillation affects the T1 andT2 signals in the same manner at the same time. Because of this, theHall sensors should be separated such that the oscillations in T1 and T2remain in phase (since they are inverted to each other). By placing theoscillations of the T1 and T2 signals in phase, the ripple effect in thecalculated torque signal is minimized. Due to mechanical packaginglimitations with regard to the locations of the sensitive areas of thetwo Hall sensors with respect to each other, a certain phase shiftexists between T1 and T2. This phase shift is shown in FIG. 3C as θ₁.FIG. 3E illustrates the T1 and T2 signals over 360 degrees with nocompensation. In this particular embodiment our goal is to minimize theoscillation in the calculated torque signal. By placing the two Hallprobes 30 degrees apart shown as θ₂ in FIG. 3D, we can put the signalsin phase to minimize the output oscillation calculated in the torquemeasurement. FIG. 3D shows the implementation of this concept in thetorque sensor. R is denoting the radial location of the Hall sensorsfrom the axis of the shaft. FIG. 3F illustrates the T1 and T2 signalsafter appropriately spacing the hall probes to minimize the ripple inthe calculated torque signal.

[0122] With particular reference to FIG. 3B, in another aspect of thepresent invention, a non-contacting position sensor 92 may be used withthe apparatus 10 for sensing the relative and/or absolute position ofthe first shaft 12 and the second shaft 14. The position sensor 92,which is shown diagrammatically, includes a ring magnet 94 magnetizeddiametrically resulting in two-pole (N-S) configuration. The ring magnet94 and the ring shield 96 are concentric with the second shaft 12 androtate therewith. The relative sensor section can detect 0˜360 degreesin either direction of rotation. A disk magnet 98 magnetized through thediameter and a ring shield 10, which are external to the ring shield 96and fixed relative to the first shaft. The disk magnet is used toprovide absolute position of the shaft since the shaft can rotate ±810degrees. The turns counter section of the sensor rotates in steps of 180degrees revolution of the first shaft or the relative sensor section andconnected there by Geneva wheel gear mechanism. In both sensor sectionthere are two Hall sensors placed at quadrature. They both use sine andcosine signals to extract position information.

[0123] The teeth 66D, 68D may have different shapes. Various examples ofteeth 66D, 68D are shown in FIGS. 8A, 8B, 8C, 8D. However, it should benoted that the present invention is not limited to any one shape of theteeth 66D, 68D.

[0124] As discussed above, the teeth 66D, 68D may be in phase or out ofphase. If the teeth 66D, 68D are in-phase or aligned, a centerline 104of the teeth 66D of the first stator plate 66 is aligned with acenterline 104 of the teeth 68D of the second stator plate 68. If theteeth 66D, 68D are out-of phase, than the centerline 104 of the teeth66D of the first stator plate 66 are offset from the centerline 104 ofthe teeth 68D of the second stator plate 68, as shown in FIGS. 3A and 4.

[0125] If the teeth 66D, 68D are out-of-phase, there may be a radial gapbetween edges of the teeth 66D, 68D as shown best in FIG. 4, the edgesof the teeth 66D, 68D may be aligned, or the teeth 66D, 68D may at leastpartially overlap.

[0126] For example, in one embodiment the edges of the teeth 66D, 68D ofone of the first and second stator plates 66, 68 are adjacent with anedge of one of the teeth 66D, 68D of the other of the first and secondplates 66, 68. The shape of the teeth 66D, 68D is shown in FIG. 8C andthe relationship between the teeth 66D, 68D is shown in FIGS. 11D and11E.

[0127] In another embodiment, at least a portion of the edge of one ofthe teeth 66D, 68D of one of the first and second plates and at least aportion of the edge of one of the teeth 66D, 68D of the other of thefirst and second plates 66, 68 overlap.

[0128] With particular reference to FIGS. 9A, 9B, 9C, 10B, 10C, 1A, 11B,and 11C, and 13-50 various, configurations of the second rotor assembly26 are shown using simple diagrammatic illustrations. Similar parts arenumbered the same.

[0129] With reference to FIGS. 9A, 9B, 9C, 10A, 10B, 10C, 11A, 11B, and11C, in another aspect of the present invention the first and secondplates 66, 68 include axial members 66E, 68E which extend in oppositedirection from the circular base 66C 68D of the first and second statorplates 66, 68, respectively to form the gap 70. In one embodiment, theaxial members 66E, 68E extend around the circumference of the circularbase 66C, 68D of each stator plate 66, 68.

[0130] With particular reference to FIGS. 9A, 9B, 9C, the teeth 66D, 68Din-phase. FIG. 9A shows a cross-section view of the teeth 66D, 68D. FIG.9B shows a top-down view of the teeth 66D, 68D. FIG. 9C shows a frontview of the teeth 66D, 68D (from the first rotor assembly 24).

[0131] With particular reference to FIGS. 10A, 10B, 10C, the teeth 66D,68D are out of phase with a gap. FIG. 10A shows a cross-section view ofthe teeth 66D, 68D. FIG. 10B shows a top-down view of the teeth 66D,68D. FIG. 10C shows a front view of the teeth 66D, 68D (from the firstrotor assembly 24).

[0132] With particular reference to FIGS. 11A, 11B, 11C, the teeth 66D,68D are out-of-phase and have the shape as shown in 8C. In thisembodiment, the edges of the teeth 66D, 68D are radially adjacent (seeabove and FIGS. 11D and 11E). FIG. 11A shows a cross-section view of theteeth 66D, 68D. FIG. 11B shows a top-down view of the teeth 66D, 68D.FIG. 11C shows a front view of the teeth 66D, 68D (from the first rotorassembly 24).

[0133]FIG. 13 shows an apparatus 10 with a first rotor assembly 24 whicha plurality of unipolar magnet 34 in first and second rows 50, 52 and asecond rotor assembly 26 with first and second stator plates 66, 68. Thefirst and second stator plates 66, 68 are planar and in phase.

[0134]FIG. 14 shows an apparatus 10 with a first rotor assembly 24 whicha plurality of unipolar magnet 34 in first and second rows 50, 52 and asecond rotor assembly 26 with first and second stator plates 66, 68 withaxial members 66E, 68E. The first and second stator plates 66, 68 are inphase.

[0135]FIG. 15 shows an apparatus 10 with a first rotor assembly 24 withtwo ring magnets 34 and a second rotor assembly 26 with first and secondstator plates 66, 68 which are planar. The first and second statorplates 66, 68 are in phase.

[0136]FIG. 16 shows an apparatus 10 with a first rotor assembly 24 withtwo ring magnets 34 and a second rotor assembly 26 with first and secondstator plates 66, 68. Each stator plate 66, 68 includes an axial member66E, 68E. The first and second stator plates 66, 68 are in phase.

[0137]FIG. 17 shows an apparatus 10 with a first rotor assembly 24 witha row of unipolar magnets 34 and a second rotor assembly 26 with firstand second stator plates 66, 68. The first and second rotor plates 66,68 are planar.

[0138]FIG. 18 shows an apparatus 10 with a first rotor assembly 24 witha row of unipolar magnets 34 and a second rotor assembly 26 with firstand second stator plates 66, 68. The first and second stator plates 66,68 include an axial member 66E, 68E. the first and second rotor plates66, 68 are out of phase.

[0139]FIG. 19 shows an apparatus 10 with a first rotor assembly 24 withfirst and second rows 50, 52 of unipolar magnets 34 and a second rotorassembly 26 with first and second stator plates 66, 68. The first andsecond stator plates 66, 68 are out of phase.

[0140]FIG. 20 shows an apparatus 10 with a first rotor assembly 24 withfirst and second rows 50, 52 of unipolar magnets 34 and a second rotorassembly 26 with first and second stator plates 66, 68. The first andsecond stator plates 66, 68 are out of phase and include an axial member66E, 68E.

[0141]FIG. 21 shows an apparatus 10 with a first rotor assembly 24 witha ring magnet 34 and a second rotor assembly 26 with first and secondstator plates 66, 68. The first and second stator plates are out ofphase and planar.

[0142]FIG. 22 shows an apparatus 10 with a first rotor assembly 24 witha ring magnet 34 and a second rotor assembly with first and secondstator plates 66, 68. The first and second stator plates are out ofphase and include an axial member 66E, 68E.

[0143]FIG. 23 shows an apparatus 10 with a first rotor assembly 24 withtwo ring magnets 34 and a second rotor assembly 26 with first and secondstator plates 66, 68. The first and second stator plates 66, 68 are outof phase and planar.

[0144]FIG. 24 shows an apparatus 10 with a first rotor assembly 24 withtwo ring magnets 34 and a second rotor assembly 26 with first and secondstator plates 66, 68. The first and second stator plates 66, 68 are outof phase and include an axial member 66E, 68E.

[0145] With reference to FIG. 25-32 in another aspect of the presentinvention, the first and second stator plates 66, 68 may include axiallyextending teeth 66F, 68F. The axially extending teeth 66F, 68F may beinterleaved or non-interleaved.

[0146]FIG. 25 shows an apparatus 10 with a first rotor assembly 24 witha plurality of unipolar magnets 34 arranged in first and second rows 50,52 and a second rotor assembly 26 with first and second stator plates66, 68. The first and second stator plates 66, 68 are in phase. Eachstator plate 66, 68 includes an axially extending member 66E, 68E and aplurality of axially extending teeth 66F, 68F. The axially extendingteeth 66F, 68F are non interleaving.

[0147]FIG. 26 shows an apparatus 10 with a first rotor assembly 24 withtwo ring magnets 34 and a second rotor assembly 26 with first and secondstator plates 66, 68. The fist and second stator plates 66, 68 are inphase. Each stator plate 66, 68 includes an axially extending member66E, 68E and a plurality of axially extending teeth 66F, 68F. Theaxially extending teeth 66F, 68F are non interleaving.

[0148]FIG. 27 shows an apparatus 10 with a first rotor assembly 24 witha plurality of unipolar magnets 34 arranged in first and second rows 50,52 and a second rotor assembly 26 with first and second stator plates66, 68. The first and second stator plates 66, 68 are out of phase. Thefirst and second stator plates 66, 68 are planar and include a pluralityof axially extending teeth 66F, 68F. The axially extending teeth 66F,68F are interleaving. Alternatively, a single row of magnets 34 may beprovided.

[0149]FIG. 28 shows an apparatus 10 with a first rotor assembly 24 witha plurality of unipolar magnets 34 arranged in first and second rows 50,52 and a second rotor assembly 26 with first and second stator plates66, 68. The first and second stator plates 66, 68 are out of phase. Eachstator plate 66, 68 includes an axially extending member 66E, 68E and aplurality of axially extending teeth 66F, 68F. The axially extendingteeth 66F, 68F are interleaving. Alternatively, a single row of magnets34 may be provided.

[0150]FIG. 29 shows an apparatus 10 with a first rotor assembly 24 witha ring magnet 34 and a second rotor assembly 26 with first and secondstator plates 66, 68. The first and second stator plates 66, 68 are outof phase. The stator plates 66, 68 include a plurality of axiallyextending teeth 66F, 68F. The axially extending teeth 66F, 68F areinterleaving.

[0151]FIG. 30 shows an apparatus 10 with a first rotor assembly 24 witha ring magnet 34 and a second rotor assembly 26 with first and secondstator plates 66, 68. The first and second stator plates 66, 68 are outof phase. Each stator plate 66, 68 includes an axially extending member66E, 68E and a plurality of axially extending teeth 66F, 68F. Theaxially extending teeth 66F, 68F are interleaving.

[0152]FIG. 31 shows an apparatus 10 with a first rotor assembly 24 withfirst and second ring magnets 34 and a second rotor assembly 26 withfirst and second stator plates 66, 68. The stator plates 66, 68 are outof phase and include a plurality of axial extending teeth 66F, 68F. Theaxial extending teeth 66F, 68F are interleaving.

[0153]FIG. 32 shows an apparatus 10 with a first rotor assembly withfirst and second ring magnets 34 and a second rotor assembly 26 withfirst and second stator plates 66, 68. The first and second statorplates 66, 68 are out of phase. The first and second stator plates 66,68 include axial extending members 66E, 68E and a plurality of axialextending teeth 66F, 68F. The axially extending teeth 66F, 68F areinterleaving.

[0154] In another aspect of the present invention the first and secondstator plates 66, 68 include a plurality of inwardly extending angularteeth 66G, 68G or outwardly extending angular teeth 66H, 68H. FIGS.33-50 show diagrammatic illustrations of an apparatus with eitherinwardly extending angular teeth 66G, 68G or outwardly extending angularteeth 66H, 68H. The illustrations show first and second stator plates66, 68 which are either in phase or out of phase, interleaving or notinterleaving teeth 66G, 68G, 66H, 68H and the various magnetarrangements.

[0155] Obviously, many modifications and variations of the presentinvention are possible in light of the above teachings. The inventionmay be practiced otherwise than as specifically described within thescope of the appended claims.

What is claimed is:
 1. An apparatus for measuring the relativedisplacement between a first shaft and a second shaft, comprising: afirst rotor assembly being coupled to the first shaft and being centeredon an axis; at least one magnet having a magnetic field and beingdisposed on the first rotor assembly; a second rotor assembly beingcoupled to the second shaft, the first and second rotor assemblies beingcoaxial, the second rotor assembly having a first stator plate and asecond stator plate, each of the first and second stator plates havingan upper surface and a lower surface, the upper and lower surfaces beingparallel, the first and second stator plates having a plurality of teethextending in a direction radial of the axis, each tooth having uppersurface and a lower surface, the upper surface of each tooth beingplanar with the upper surface of the respective stator plate, the lowersurface of each tooth being planar the lower surface of the respectiveplate, the first and second stator plates forming a gap between thelower surface of the first stator plate and the upper surface of thesecond stator plate, the gap having a uniform thickness; and, a sensingdevice disposed within the gap for sensing a magnetic flux of themagnetic field.
 2. An apparatus, as set forth in claim 1, furthercomprising a compliant member coupled between the first and secondshafts for allowing relative movement therebetween.
 3. An apparatus, asset forth in claim 1, further comprising a retaining member to hold thefirst and second stator plates and fixing the relative position thereof,respectively, and being fixedly coupled to the lower shaft.
 4. Anapparatus, as set forth in claim 3, each stator plate including acircular base section, the plurality of teeth extending from thecircular base section.
 5. An apparatus, as set forth in claim 1, themeasuring device being mounted to a stationery member or to a bearingsurface.
 6. An apparatus, as set forth in claim 3, the retaining memberincluding a bore for being press-fit onto the second shaft.
 7. Anapparatus, as set forth in claim 3, the retaining member being made froma non-magnetic material.
 8. An apparatus, as set forth in claim 3, theretaining member being made from plastic.
 9. An apparatus, as set forthin claim 3, the first and second stator plates being glued and/orcrimped to the retaining member.
 10. An apparatus, as set forth in claim3, the retaining member being overmolded the first and second statorplates.
 11. An apparatus, as set forth in claim 1, wherein the first andsecond stator plates are made using a stamping process or a metalinjection molding process or a casting process.
 12. An apparatus, as setforth in claim 1, wherein the first and second stator plates are madefrom a powdered metal using a sintering or bonding process.
 13. Anapparatus, as set forth in claim 1, the first rotor assembly having acircumference and a plurality of slots spaced evenly around thecircumference, the apparatus including a plurality of magnets, eachmagnet being located in one of the slots
 14. An apparatus, as set forthin claim 13, the plurality of magnets being uni-polar.
 15. An apparatus,as set forth in claim 13, each magnet having first and second parallelsurfaces and four side surfaces, the first and second parallel surfacesbeing parallel to the axis, at least one pair of opposite edges formedby one of the side surfaces and the first parallel surface beingrounded.
 16. An apparatus, as set forth in claim 13, each magnet havingfirst and second parallel surfaces and four side surfaces, the first andsecond parallel surfaces being parallel to the axis, the first andsecond parallel surfaces being rectangular.
 17. An apparatus, as setforth in claim 13, each magnet having first and second parallel surfaceand four side surfaces, the first and second parallel surfaces beingparallel to the axis, the first and second parallel surface beingsquare.
 18. An apparatus, as set forth in claim 13, the plurality ofmagnets being in a single row around the circumference of the firstrotor assembly.
 19. An apparatus, as set forth in claim 13, theplurality of magnets being in two rows around the circumference of thefirst rotor assembly.
 20. An apparatus, as set forth in claim 1, thefirst rotor assembly having a circumference, the at least one magnetbeing a ring magnet.
 21. An apparatus, as set forth in claim 20, furthercomprising a second ring magnet, the first and second ring magnets beingin parallel planes perpendicular to the axis.
 22. An apparatus, as setforth in claim 1, further comprising a second sensing device having adisplacement from the other sensing device such that any changes inmagnetic flux at constant displacement between the first and secondrotor assemblies over 360 degrees will have the same effect on eachdevice.
 23. An apparatus, as set forth in claim 1, the teeth of thefirst and second stator plates being in phase.
 24. An apparatus, as setforth in claim 1, the teeth of the first and second plates being out ofphase.
 25. An apparatus, as set forth in claim 24, an edge of one of theteeth of one of the first and second plates being adjacent with an edgeof one of the teeth of the other of the first and second plates.
 26. Anapparatus, as set forth in claim 25, at least a portion of the edge ofone of the teeth of one of the first and second plates and at least aportion of the edge of one of the teeth of the other of the first andsecond plates overlapping.
 27. An apparatus, as set forth in claim 25,at least a portion of the edge of one of the teeth of one of the firstand second plates and at least a portion of the edge of one of the teethof the other of the first and second plates forming a gap.
 28. A rotorassembly for use in a sensor for measuring relative displacement betweenfirst and second shafts, comprising: a first stator plate having anupper surface and a lower surface, the upper and lower surfaces beingparallel; a second stator plate having an upper surface and a lowersurface, the upper and lower surfaces of the second stator plate beingparallel, the first and second stator plates having a plurality ofteeth, the first and second stator plates forming a gap between thelower surface of the first stator plate and the upper surface of thesecond stator plate; and, a retaining member to hold the first andsecond stator plates, respectively.
 29. An apparatus, as set forth inclaim 28, each stator plate including a circular base section, theplurality of teeth extending from the circular base section.
 30. Anapparatus, as set forth in claim 28, the retaining member substantiallyenclosing the first and second stator plates for fixing the relativeposition thereof.
 31. An apparatus, as set forth in claim 28, theretaining member being made from a non-magnetic material.
 32. Anapparatus, as set forth in claim 28, the teeth of the first and secondstator plates being in phase.
 33. An apparatus, as set forth in claim28, the teeth of the first and second plates being out of phase.
 34. Anapparatus, as set forth in claim 28, the teeth extending in a directionradial of an axis, each tooth having upper surface and a lower surface,the upper surface of each tooth being planar with the upper surface ofthe respective stator plate, the lower surface of each tooth beingplanar the lower surface of the respective plate.
 35. An apparatus, asset forth in claim 28, the retaining member being overmolded the firstand second stator plates.
 36. An apparatus, as set forth in claim 28,the first and second stator plates being glued and/or crimped to theretaining member.
 37. A rotor assembly for use in an apparatus formeasuring the relative position between first and second shafts,comprising: a rotor centered on an axis, the rotor having an innersurface and an outer surface, the outer surface forming at least oneslot associated with an outer radius, the inner surface forming at leastone support structure associated with an inner radius, the inner radiusbeing larger than the outer radius; and, at least one magnet disposed inthe at least one slot.
 38. A rotor assembly, as set forth in claim 37,further comprising a retaining member surrounding the rotor assembly forretaining or adhering the at least one magnet in the respective slot.39. A rotor assembly, as set forth in claim 38, the retaining memberbeing made from a non-magnetic material.
 40. A rotor assembly, as setforth in claim 37, the rotor having a circumference and a plurality ofslots spaced evenly around the circumference, the rotor assemblyincluding a plurality of magnets located in one of the slots.
 41. Arotor assembly, as set forth in claim 40, the plurality of magnets beinguni-polar and in a single row around the circumference of the firstrotor assembly.
 42. An apparatus, as set forth in claim 40, theplurality of magnets being in two rows around the circumference of thefirst rotor assembly.
 43. An apparatus, as set forth in claim 40, the atleast one magnet being a ring magnet.
 44. An apparatus, as set forth inclaim 38, the retaining member being overmolded the rotor and at leastone magnet.
 45. An apparatus, as set forth in claim 37, the rotor havinga non-continuous inner diameter.
 46. An apparatus, as set forth in claim37, wherein hoop stress is eliminated in the rotor assembly by havingthe inner radius larger than the outer radius and a non-continuous innerdiameter.